At least four people have been killed in a suicide car bomb attack in central Mogadishu. According to an official and witnesses, the car blew up before the security forces were able to inspect it. Sunday's attack was the second car bombing this week in the Somali capital. The one on Thursday outside a popular hotel killed 14 people. Al-Qaeda-affiliated Shabaab jihadists have claimed responsibility for both attacks. Mogadishu is regular target for al-Shabaab, which seeks to overthrow the internationally-backed government. In February, twin car bombings left 38 people dead. Last October saw Somalia's deadliest-ever attack. More than 500 people were killed in a truck bombing in a busy part of the city.